30 September 2019
A simple guide to impedance matching for RF
12 August 2019
Embedded antennas will perform differently from device-to-device, depending on various design factors. Due to this difference, over-the-air (OTA) testing is critical. Without a rigorous testing stage, a device can perform poorly or fail to work.
Within some markets, new designs are subject to rigorous testing by certification bodies and cellular networks. In the United States, wireless devices are required to obtain both PTCRB certification and network approval (from the likes of AT&T, Verizon) in order to launch. In each geography, the requirements can differ. By comparison, European network approval standards are far more relaxed than in North America. So this is something that needs to be factored into the design process.
Certification can be expensive, costing anywhere upwards of tens of thousands of dollars in total. To make matters worse, if a device fails, the whole process typically resets. Most certification programs do not offer the opportunity to retest a device that has previously failed. This can add time delays and quickly cause project costs to spiral. And that, is where pre-certification over-the-air (OTA) testing comes in.
Optimising an embedded antenna for performance can be a delicate procedure. Radio frequency energy can be disrupted by nearby components, mismatched transmission lines, insufficient ground plane dimensions, and these factors are all determined in a design. There are also a number of in-situ variables that come into play, too. Such as the presence of body parts and other interfering signals that can detune an antenna away from its optimal frequency.
OTA testing helps identify and counteract these issues before a device heads to market. It helps improve wireless performance, keep project costs down and reduces the chance of unanticipated delays.
While choosing an antenna, data sheets are good indicators of an antennas characteristics and performance in free space. Over-the-air tests are perfect for assessing the performance of an antenna when it has been integrated within a device. These provide indicators of performance in terms of efficiency, spurious emissions and return loss.
Efficiency is one of the most widely cited measures of RF performance. It’s important as it describes the ratio of power radiated by the antenna, compared to the power delivered to it. Antennas are typically designed to operate over a wide berth of frequencies, which means there are certain frequencies where a specific antenna excels. More efficient performance helps reduce battery drainage caused by wireless communications.
Pattern measurements, like directivity, describe the directional characteristics of an antenna. It shows how RF energy is transmitted from the antenna. This is useful to know in the case of handheld and wearable devices. As users are likely to interact with the device in a certain way that allows the antenna placement to be optimised. For example, in a wearable, the directivity should be focused away from the user.
An antenna’s gain is a measure of how much of the antennas radiation is emitted in a single direction. A higher gain is most useful when the antennas are required to have directional characteristics.
The Total Radiated Power (TRP) is a measure of how much power is radiated by an antenna. The measurement is taken isotropically, i.e the antennas total received power is calculated and summed up over all possible directions.
The term spurious emissions refers to any radio frequency not deliberately created or transmitted by a device. To make sure your product adheres to regulatory standards, it is imperative to measure spurious emissions. More so than others, RSE tests are difficult to pass, particularly for cellular devices. Spurious emissions, which can affect the performance of other devices, might undermine the saleability of your device. Identifying spurious emissions will help you determine any design or regulatory issues and avoid project delays or excess manufacturing costs.
Over-the-air testing is a critical feature of successful wireless projects. Not only do they help improve the performance of a device, but they can be used to reduce network approval costs, reduce the time-to-market and diagnose performance issues before a product reaches consumers.
Antenova’s anechoic testing facilities feature best in class equipment, including an anechoic chamber, phantom body parts and other testing equipment. For more information about our testing facilities, download our service sheet on OTA testing. If you have a completed design that is ready to be tested, get in touch with your local Antenova representative to learn more.